Process of making photographs in natural colors.



R. FISCHER.

rnocnss OF MAKING PHOTOGRAPHS IN NATURAL COLORS.

I APPLICATION FIPLED JULY 1, 1912, 1,055, 1 55, Patented'Mar. 4, 1913.

[NVENTOR reduced silver.

RUDOLF FISCHER, OF STEGLITZ, NEAR BERLIN, GERMANY.

PROCESS OF MAKING PHOTOGRAPHS IN NATURAL COLORS.

Specification of Letters Patent.

Patented Mar. 4,1913.

Application filed July 1, 1912. Serial No. 707,084.

To all whom it may concern Be it known that I, RUDOLF FISCHER, a citizen of the Empire of Germany, and residing at Steglitz, near Berlin, Germany, have invented a certain new and useful Improved Process of Making Photographs in Natural Colors, of which the following is a specification.

My invention relates to processes of making photographs in natural colors.

It is well known that by bathing exposed films "of halogen-silver in suitable solutions monochrome pictures can be directly obtained, the exposed halogen-silver oxidizing the substance in the solutions to an insoluble coloring-matter which is precipitated on the Hereinafter this mode of development will be termed color development, and the substances causing the same color formers.

In the process according to my invention I utilize this stronger oxidation capacity of exposed halogen-silver as compared with that of unexposed for producing colored photographs. I can do this in various ways, and both additive as well as subtractive colored pictures can be produced equally well.

I. For example, to make an additive colored picture, I expose a halogen-silver layer sensitive to light'under a screen, onethird of whose surface is permeable to light while two-thirds thereof are covered, then bathe the layer in a solution, 6. g. indoxyl, producing a blue coloring-matter, then expose it under a second screen, one-third of the surface being again exposed, and then bathe it in a solution, 6. g. thioindoxyl, producing a red coloring-matter. I then expose the whole surface without the screen-negative, the remaining or previously unexposed halogen-silver being influenced and colored green when bathed in a solution, 6. g. chlorid of indoxyl, producing a green coloring-matter. During the second and third exposures the reduced silver and. the particles of such coloring matter protect the unchanged halogen-silver below it from further exposure and develo ment. Moreover, this protect-ion can be a orded by the coloring-matter already formed, by using during the subse quent exposures a light which is absorbed by the existing coloring-matter. The reduced silver is then removed with e. g. Farmers reducing solution and the unchanged halogensilver with a fixing agent.

II. For subtractive pictures I employ, as

usual, three part-negatives, each of which corresponds to one of the primary colors. From these negatives three part-positives are produced on halogen-silver layers, then developed as above described with the cor.-

.responding color-formers, and finally placed one above another. The part-positives can also be obtained directly from a complementary-colored negative produced by means of screens by making positive part-extracts from the negative either using filters and copying on a panchromatichalogen-silver layer, or without filters and copying on selectively-sensitized halogen-silver layers. These positives are developed colored and superposed one on another as described above.

The last described process of reproduction on three selectively-sensitized halogensilver emulsions can be carried out in one operation in the following manner :Three emulsions are made, one being. sensitive only to blue, another only to green and a third only to red. In these emulsions are incorporated the substances necessary for the formation of each color, i. e. the substances termed color formers, the latter being so selected, for example, .that that color is formed at any time which is complementar to the corresponding selective color-sensitization of the halogen-silver. Now when these three emulsions are poured out in three layers one on another, there is formed, 0. 9. under the action of blue light, a yellow color, and at the places acted on by red or green light the corresponding complementary colors. When the colors are correctly chosen those places which white light strikes become nearly black, while at those Whereon no light strikes, (2'. 6. under the covered parts of the negative), no coloration is formed at all, and consequently after fixing white results. 'By copying a complementary-colored negative on such a layer the correct colors and correct black-white values are obtained. As such superposed layers are very thin they will actually stop only light rays of their own color.

Instead of pouring the three above emulsions in three layers one on another, before pouring them I may treat them in a suitable 1 manner, 6. g. by tanning, so that they can be mixed without the three complexes (halogen-silver and color-formers) uniting to form one homogeneous layer or film; this treatment has heretofore been proposed for a theoretically developed process of color photography. (Photographz'sche R'zmdsohau 1911, page 2.)

The halogen-silver which is unchanged during the copying operation and the silver formed simultaneously with the coloringmatter are removed by fixing and reducing agents.

When practising the process with three layers, 1' may use a yellow coloring-matter mixed with a binder as an intermediate layer for the purpose of reducing the sensitiveness to blue in the layers of halogensilver sensitive to green and red. It is,

moreover, preferable not to pour the three film directly one on another, but to interpose -a colorless layer in order to prevent diffusion of the color-producing substances.

Example: Witha complementary-colored screen-negative an exposure is made through a blue-filter on a transferable panchromatic layer of halogen-silver. ture is developed with pyrogallol, fixed, and the silver removed with Farmers reducing agent. This yellow part-picture is now drawn off and transferred to a suitable backing. An exposure is then made with a green filter on a similar layer and a purplered picture developed in the following developer: 0.5 g. thioindoxyl carboxylic acid, 5 c. cms. acetone, 5 g. potash, and 100 c. cms. water. After fixing and removing the silver, this redv picture is transferred to the yellow one. Finally, by using a red filter an exposure is made on a panchromatic layer and-this is developed in the following developer: 0.5 g. indoxyl carboxylic acid, 5

. c. cms.-acetone, 2 g. potash, 100 c. cms. water.

After the removal of the silver and halogensilver this pictureis transferred to the two former pictures.k,.f-

' QE J In the accompanying-drawingsFigure 1 is a plan view of an undeveloped plate or film indicating the several' l-laiyers of emulsion. Fig. 2 is a magnified edge view of- The exposed picplate.

In the drawings the different layers of emulsions are indicated. in Figs. 1 and 2 by the letters a, b and 0. a being the blue emulsion; b'the green; and c the red emulpyrogallol the green one I) with thloindoxyl carboxylic acid; and the red layer cwith indoxyl carboxylic acid. V v

- Fig. 3 shows at a the 'elfect of-exposure second exposure of the plate; and Fig. '5

developed by a third exposure; and it also shows the completed photograph.

' I claim 1. The herein described processof makexposed halogen-silver film by developing such film by means of such substances as are oxidized by exposed halogen-silver to colored substances soluble with difliculty.

RUDOLF FISCHER Witnesses:

VVOLDEMAR HAUPT, HENRY HASIER.

such a plate. Figs. 3, 4 and 5 show the several steps of the development. of the'picture by successive exposures of the prepared sion. The blue layer a is develo' ed with of the blue layer a. Fig. 4 showsat b the efi'ect of'exposing the green layer 1) by ashows at'c how the red layer a has been 7 ing colored photographs consisting in producing the various primary colors on an 2. A process of making colored photo- 

